Apologies if this has been brought up before:
Per Wikipedia: Lafayette has a population of 120,623 as of the 2010 census.
Ford F-series trucks (if that is what it is) have been the best selling truck for over 30 years.
Even though that's a large population, and the truck is popular, I still don't think that many white trucks of similar style will be on the roads at that time of night.
My personal experience - I go to work very early in the AM, 4AM, and I might see only a few of these over a 30 mile stretch of interstate. Of course I'm in a completely different area.
What is the nightlife like in Lafayette? Do bars, *advertiser censored* shops, clubs, other stores, close at a certain time?
What are likely popular destinations somebody with no bad motive would be driving, along the routes mentioned, at that time of the AM?
Edit: I'm sure the theory that she was possibly hit and the driver freaked out has been brought up? Are there significant wooded areas or bodies of water for evidence to be dumped in the area?